1. Field of the Invention
The present invention relates to a modified polybutene or polyisobutylene polymer and a rubber composition containing the same. More specifically, it relates to a modified polybutene or polyisobutylene having the improved tan xcex4 balance of a rubber composition when compounded into a rubber composition (i.e., the tan xcex4 at 0xc2x0 C. is increased and the tan xcex4 at 60xc2x0 C. is decreased), having the improved reinforcing effect of a filler such as carbon black, and having the improved abrasion resistance and also relates to a rubber composition containing the same, in particular a rubber composition useful as a tire tread of a pneumatic tire.
2. Description of the Related Art
A polymer containing isobutylene as a monomer, in particular, a so-called butyl rubber, exhibits a high grip property since the tan xcex4 is higher over a broad range of a temperature and is believed to improve the wet braking performance since the tan xcex4 at 0xc2x0 C. is high. However, polymers containing isobutylene as a monomer have a small amount of double bonds in the molecule, and therefore the reinforcement with the carbon black is not sufficient and, as a result, the abrasion resistance is inferior.
On the other hand, these polymers have been developed as rubber compositions for pneumatic tires, in particular, tire treads. Under these circumstances, it is known in the art that an oil such as an aromatic oil is added to the rubber composition at the time of compounding the rubber for the purposes of reducing costs, improving the processability (i.e., reducing the viscosity of the composition), improving the physical properties (i.e., reducing the modulus and raising the elongation), etc. However, the addition of an oil has the problem that the compounded oil easily bleeds out from the vulcanized product and decreases the vulcanized rubber properties (e.g., tan xcex4 balance and abrasion resistance).
Accordingly, an object of the present invention is to eliminate the problems of a polymer containing isobutylene as a monomer, such as the above-mentioned conventional butyl rubber, and to provide a modified polybutene(polyisobutylene) which is useful for a rubber composition, having a high tan xcex4 at 0xc2x0 C. (i.e., is superior in wet braking property) and has a low tan xcex4 at 60xc2x0 C. (i.e., is superior in fuel consumption) and which is superior in the balance of the tan xcex4, without substantially reducing the abrasion resistance, and to a rubber composition containing the same.
Another object of the present invention is to provide a rubber composition which is capable of solving the problems of the above-mentioned conventional oil-formulated rubber composition, is capable of improving the processability of the rubber composition due to the softening effect thereof, and has the superior tan xcex4 balance and the improved abrasion resistance.
A further object of the present invention is to provide a modified polybutene(polyisobutylene) which is useful for a tire, having the improved reinforcing properties, viscoelastic properties and abrasion resistance, and to provide a rubber composition containing the same.
In accordance with the present invention, there is provided a polymer comprising isobutylene repeating units and having backbone, at the ends, and/or at the side chains of the molecule thereof, at least one free radical selected from the group consisting of nitroxide radicals, hydrazyl radicals, aryloxy radicals, and trityl radicals stably present at a room temperature and in the presence of oxygen.
In accordance with the present invention, there is also provided a modified polybutene(polyisobutylene) comprising isobutylene as repeating units and having, in the backbone, at the ends, and/or at the side chains of the molecule thereof, at least one structure selected from the group consisting of (A) a half-ester structure, (B) an amic acid structure, (C) an onium salt structure, and (D) an imide structure, and a rubber composition containing said modified polymer.
In accordance with the present invention, there is further provided a rubber composition comprising 100 parts by weight of at least one starting diene rubber, at least 20 parts by weight of at least one filler, and 0.1 to 80 parts by weight of at least one acid anhydride-modified polybutene containing 50 mol % or more of isobutylene unit and having an alkenyl group.
In accordance with the present invention, there is further provided a polymer comprising isobutylene, as at least one monomer, and having an alkoxysilane and at least one hydrogen bondable moiety selected from the group consisting of a carboxylic acid, amide, ester, hydroxyl group and amino group in the molecule thereof.
According to the first aspect of the present invention, as explained above, by introducing into the polybutene(polyisobutylene), preferably the end of the polymer thereof, a free radical compound stable at a room temperature and in the presence of oxygen, when the main chain of the starting rubber is radically cut, the cut radicals of the rubber are trapped with the free radicals and a block copolymer is produced in the system. This block copolymer has a high double bond content, and therefore interacts with the carbon black and, as a result, the reinforcing effect of the carbon black is increased. Therefore it is possible to increase the tan xcex4 at 0xc2x0 C. and to decrease the tan xcex4 at 60xc2x0 C., without substantially decreasing the abrasion resistance.
According to the present invention, preferably free radicals stably present at a room temperature and in the presence of oxygen are introduced into the polymer having the isobutylene as repeating units, preferably into the chain ends. Examples of such free radicals are nitroxide radicals, hydrazyl radicals, aryloxy radicals, and trityl radicals. Further, as the polymer having the isobutylene as repeating units, that is, the polymer obtained from the polymerization of isobutylene as a monomer, polyisobutylene, polybutene, butyl rubber, brominated butyl rubber, isobutylene maleate anhidride copolymer, isobutylene-p-methyl styrene-p-bromomethyl styrene copolymer, etc. are known. Of course, the polymer of the present invention is not intended to limit to these polymers.
According to the present invention, as shown in the Production Examples I-1 to I-3 below, it is possible to obtain the desired polymer by reading a polymer having isobutylene as repeating units with a compound having the free radicals. In the reaction, it is preferable to react the polymer having the isobutylene as repeating units with the free radical compound at a desired position, for example, at the end of the polymer chain, and modify the same with any reactive group so as to cause the bonding of the free radicals. Examples of such reactive groups are an alkoxysilyl group, acid anhydride group, ester group etc. These may be appropriately determined by a person skilled in the art. Further, the reaction conditions are not particularly limited.
The polybutene(polyisobutylene) according to the present invention is compounded into 100 parts by weight of a rubber generally used as a rubber composition in the past, especially, a starting diene rubber, in an amount of 0.1 to 100 parts by weight, preferably 1 to 30 parts by weight. If the content is too small, there is a tendency for no substantial additional effect, whereas if too large, the mixablility and rollability tend to be poor and the bleeding is caused, after vulcanization, to thereby remain a tack.
When mixing the silica into the rubber composition according to the present invention, in the same way as in the prior art, for example, it is possible to use a silane coupling agent in an amount of 5 to 30% by weight of the content of silica. Further, in this case, it is possible to mix a silanol condensation catalyst in an amount of 0.05 to 50% by weight of the content of the silane coupling agent. As the silane coupling agent usable for the silica-containing rubber composition according to the present invention, it is possible to select any silane coupling agent optionally used as a silica filler in the past. As typical examples, vinyl trimethoxysilane, vinyl triethoxysilane, vinyl tris(2-methoxyethoxy)silane, N-(2-aminoethyl)3-aminopropylmethyl dimethoxysilane, N-(2-aminoethyl)3-aminopropyl trimethoxysilane, 3-aminopropyl triethoxysilane, 3-glycidoxypropyl trimethoxysilane, 3-glycidoxypropylmethyl dimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane, 3-methacryloxypropyl trimethoxysilane, 3-mercaptopropyl trimethoxysilane, 3-aminopropyl trimethoxysilane, bis-[3-(triethoxysilyl)-propyl]tetrasulfide, etc. may be mentioned. Among these, bis-[3-(triethoxysilyl)-propyl]tetrasulfide is most preferred from the standpoint of the processability.
The rubber composition according to the present invention may also contain therein various additives generally mixed in for other general rubber use such as vulcanization or cross-linking agents, vulcanization or cross-linking accelerators, various types of oils, antioxidants, fillers, plasticizers, and softening agents. The mixture may be kneaded and vulcanized by a general method to produce the composition which may in turn be used for the vulcanization or cross-linking. The contents of the additives may be made the general contents of the prior art in so far as the objects of the present invention are not impaired.
The rubber composition according to the present invention may be used not only for tires, but also for belts, hoses, rubber shock absorbers, rollers, sheet linings, rubberized cloth, seal materials, gloves, fenders, and the like.
According to the second aspect of the present invention, as explained above, due to the modified polybutene(polyisobutylene) containing isobutylene as repeating units and having, in the main chain, at the ends, and/or at the side chains of the polymer thereof, at least one structure selected from the group consisting of (A) a half-ester structure, (B) an amic acid structure, (C) an onium salt structure, and (D) an imide structure, it is possible to increase the tan xcex4 at 0xc2x0 C. and to decrease the tan xcex4 at 60xc2x0 C., without substantially decreasing the abrasion resistance.
According to the second aspect of the present invention, the above-mentioned object can be achieved by introducing a half-ester structure (A), or amic acid structure (B), an onium salt structure (C), and/or an imide structure (D) into the molecule of the polymer having the isobutylene as repeating units (i.e., in the main chain, at the ends, and/or at the molecule side chains of the polymer thereof), preferably at the ends of the polymer chain.
The half-ester structure (A) (i.e., a structure having an ester group and a carboxyl group simultaneously in the molecule) is mainly comprised of a structure of the formula (I): 
wherein R1 is a C1 to C25 hydrocarbon group which may contain an oxygen atom, nitrogen atom and/or silicon atom, preferably a long-chain alkyl group such as a stearyl group.
It has been found that, by compounding into the rubber composition, a modified polybutene(polyisobutylene) containing this structure in the polymer thereof, the affinity with the filler is improved and, at the same time, the reinforcement effect is improved due to the so-called pseudo cross-linking effect caused by the hydrogen bond and the viscbelastic properties and the abrasion resistance are improved.
Further, the amic acid structure (B) (i.e., a structure having an amide group and a carboxyl group simultaneously in the molecule) is mainly composed of a structure having formula (II); 
wherein R2 and R3 are independently a hydrogen atom or a C1 to C25 hydrocarbon group which may contain an oxygen atom, nitrogen atom and/or silicon atom preferably a long-chain alkyl group such as a stearyl group.
It has been found that, by compounding into the rubber composition, a modified polybutene(polyisobutylene) containing this structure in the polymer, the affinity with the filler is improved and, at the same time, the reinforcement effect is improved due to the so-called pseudo cross-linking effect of the hydrogen bond and the viscoelastic properties and the abrasion resistance are improved.
Further, the onium salt structure (C) is mainly composed of a structure having the formula (III): 
wherein R4 and R5 are independently a hydrogen atom or a C1 to C25 hydrocarbon group which may contain an oxygen atom, nitrogen atom and/or silicon atom, preferably a long-chain alkyl group such as a stearyl group.
It has been found that, by compounding into the rubber composition, a modified polybutene(polyisobutylene) containing this structure in the polymer, the affinity with the filler is improved and, at the same time, the reinforcement effect is improved due to the so-called pseudo cross-linking effect of the hydrogen bond and the viscoelastic properties and the abrasion resistance are improved.
Further, the imide structure (D) is mainly composed of a structure having the formula (IV): 
wherein R6 is a hydrogen atom or a C1 to C25 hydrocarbon group which may contain an oxygen atom, nitrogen atom, and/or silicon atom, preferably a long-chain alkyl group such as a stearyl group.
It has been found that, by compounding into the rubber composition, a modified polybutene(polyisobutylene) containing this structure in the polymer, the affinity with the filler is improved and, at the same time, the reinforcement effect is improved due to the so-called pseudo cross-linking effect of the hydrogen bond and the viscoelastic properties and the abrasion resistance are improved.
The modified polybutene(polyisobutylene) having the structures (A) to (D) in the polymer thereof are based upon the polymers having at least one isobutylene as a monomer. Examples of such a polymer are polyisobutylene, polybutene, butyl rubber, brominated butyl rubber, isobutylene-maleic anhydride copolymer, isobutylene-p-methyl styrene-p-bromomethyl styrene copolymer, etc. The raft molecular weight thereof is not particularly limited, but in general a weight average molecular weight of 1000 to 1,000,000 is preferable. In the present invention, as shown in the Production Examples below, it is possible to modify the basic polymer by the reactive thereof with a suitable reaction agent.
According to the second aspect of the present invention, there is provided a rubber composition containing (i) 100 parts by weight of at least one starting diene rubber, (ii) at least 10 parts by weight, preferably 15 to 100 parts by weight, of at least one filler, and (iii) 0.1 to 80 parts by weight, preferably 1 to 30 parts by weight, of a modified polybutene(polyisobutylene). This rubber composition can increase the tan xcex4 at 0xc2x0 C. and decrease the tan xcex4 at 60xc2x0 C., without substantially affecting the abrasion resistance. If the content of the filler is too small, bleeding of the filler and modified polybutene is caused and, further, the mechanical properties of the rubber composition per se become poor. Further, if the content of the modified polybutene(polyisobutylene) is too small, the desired effect is not obtained. Contrary to this, if too large, the mixability and rollability become worse and tack remains after the vulcanization.
According to the second aspect of the present invention, there is further provided a rubber composition comprising (i) 100 parts by weight of at least one type of diene-based rubber, (ii) at least 10 parts by weight, preferably 15 to 100 parts by weight, of at least one type of filler, (iii) 0.1 to 80 parts by weight, preferably 1 to 30 parts by weight, of at least one modified polybutene(polyisobutylene), and (iv) 0.1 to 80 parts by weight, preferably 1 to 30 parts by weight, of (a) a polybutene(polyisobutylene) containing isobutylene as repeating units and modified with an acid anhydride group and/or (b) a modified polybutene(polyisobutylene) containing isobutylene as repeating units and having in A the polymer thereof at least one free radical selected from the group consisting of nitroxide radicals, hydrazyl radicals, aryloxy radicals, and trityl radicals stably present at a room temperature and in the presence of oxygen. This rubber composition also similarly improves the affinity with the filler and, at the same time, improves the reinforcement and is excellent in viscoelastic properties.
Also, in this composition, if the content of the filler is too small, bleeding of the modified polybutene is caused and, further, the mechanical properties of the rubber composition per se become poor. Further, if the content of the modified polybutene(polyisobutylene) (iii) is too small, the desired effect cannot be obtained. Conversely, if too large, the mixability and rollability become worse and tack remains after the vulcanization. Further, if the content of the modified polybutene(polyisobutylene) (iv) is too small, the desired effect cannot be obtained, whereas conversely if too large, the mixability and rollability become worse and tack remains after the vulcanization.
The modified polybutene(polyisobutylene) having, in the polymer having isobutylene as repeating units used in the present invention, preferably at the chain ends, nitroxide radicals, hydrazyl radicals, aryloxy radicals, and trityl radicals stably present at a room temperature and in the presence of oxygen can be obtained, as shown in, for example, the Production Examples below, can be obtained by the reaction between a polymer having isobutylene as repeating units and a compound having the free radicals. In the reaction, it is preferable to react the polymer having the isobutylene as repeating units with the free radical compound at a desired position, for example, the ends of the polymer chain, and modify the same with any reactive group so as to cause the bonding of the free radicals. Example of the reactive group are an alkoxysilyl group, acid anhydride group, ester group, etc. These reactions may be appropriately determined by a person skilled in the art. Further, the reaction conditions are not particularly limited either.
The polybutene(polyisobutylene) modified with the acid anhydride group, are those mainly composed of a maleic anhydride-modified polybutene having the formulae (V) to (VIII): 
wherein R is a C4 hydrocarbon fraction and n is an integer of 1 to 1000.
The term xe2x80x9cpolybutenexe2x80x9d used herein means a compound produced by polymerizing a C4 hydrocarbon fraction obtained from the cracking of naphtha etc. and containing isobutylene, 1,2-butene, 2,3-butene, etc. in the presence of a catalyst such as boron trifluoride or aluminum chloride. Those having the hydrogenated double bonds in the polybutene may also be used. The R in the formulae (V) to (VIII) preferably is mainly composed of xe2x80x94CH2xe2x80x94C(CH3)2xe2x80x94 and contains a small amount of xe2x80x94CH2xe2x80x94CH(C2H5)xe2x80x94 or xe2x80x94CH(CH3)xe2x80x94CH(CH3)xe2x80x94 etc.
The maleic anhydride units having formulae (V) to (VIII) may be introduced by a conventional method, for example, the reaction between the end of olefin and the maleic anhydride, whereby the maleic anhydride unit is introduced into polyisobutylene by an Ene reaction under heating and stirring conditions. When the acid anhydride-modified polybutene thus obtained is compounded., the maleic anhydride units react with, for example, the hydroxy groups or carbonyl groups etc. on the carbon black to thereby bond with the carbon black. On the other hand, the isobutylene units improve the tan xcex4 balance (and abrasion resistance). If the content of the acid anhydride modified polybutene is too small, the desired effect cannot be obtained, whereas if too large, the mixability and rollability become worse and tack remains after the vulcanization.
The starting rubber used, as the main component, in the rubber composition according to the present invention is any diene rubber generally used in various rubber compositions in the past. For example, natural rubber (NR), polyisoprene rubber (IR), various styrene-butadiene copolymer rubbers (SBR), various polybutadiene rubbers (BR), acrylonitrile-butadiene copolymer rubbers (NBR), butyl rubber (IRI), and other diene-based rubbers may be used alone or in any blends thereof.
The rubber composition according to the present invention further contains a general filler. Examples of such a filler are carbon black, silica, etc. At least 10 parts by weight, preferably 15 to 100 parts by weight, more preferably 30 to 70 parts by weight, of the filler are compounded into 100 parts by weight of the diene rubber. If the content of the filler is too small, the reinforcement required for the rubber composition cannot be obtained.
The isobutylene-based polymer according to the present invention may also be used mixed into the rubber after first reacting with the filler such as the carbon black or silica (bulk or solution).
When blending silica into the rubber composition according to the present invention, like in the past, for example, it is possible to blend in 5 to 30% by weight of a silane coupling agent with respect to the content of the silica. Further, in this case, it is possible to blend a silanol condensation catalyst in an amount of 0.05 to 50% by weight of the content of the silane coupling agent. As the silane coupling agent used for the silica-containing rubber composition according to the present invention, it is possible to use any silane coupling agent used as a silica filler in the past.
As typical examples, vinyl trimethoxysilane, vinyl triethoxysilane, vinyl tris(2-methoxyethoxy)silane, N-(2-aminoethyl)3-aminopropylmethyl dimethoxysilane, N-(2-aminoethyl)3-aminopropyl trimethoxysilane, 3-aminopropyl triethoxysilane, 3-glycidoxypropyl trimethoxysilane, 3-glycidoxypropylmethyl dimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane, 3-methacryloxypropyl trimethoxysilane, 3-mercaptopropyl trimethoxysilane, 3-aminopropyl trimethoxysilane, bis-[3-(triethoxysilyl)-propyl]tetrasulfide, etc. may be mentioned. Among these, bis-[3-(triethoxysilyl)-propyl]tetrasulfide is most preferred from the standpoint of the processability.
The rubber composition according to the present invention may contain thereof, in addition to the above essential ingredients, various additives generally mixed in for tire use or other general rubber use such as vulcanization or cross-linking agents, vulcanization or cross-linking accelerators, various types of oils, antioxidants, and plasticizers. The mixture may be kneaded and vulcanized by a general method to produce the composition which may in turn be used for the vulcanization or cross-linking. The contents of the additives may be made the general contents of the prior art in so far as the objects of the present invention are not impaired.
The rubber composition according to the present invention may be used not only for tires, but also for belts, hoses, rubber shock absorbers, rollers, sheet linings, rubberized cloth, seal materials, gloves, fenders, and the like.
The rubber composition according to the third aspect of the present invention is suitable for use as a tire tread and contains, as essential ingredients, a diene rubber, a filler for rubber, and acid anhydride-modified polybutene.
The rubbers compounded into the rubber composition according to the third aspect of the present invention are diene rubber generally used in rubber compositions in the past, in particular, those for tires. Specifically, for example, natural rubber (NR), various butadiene rubbers (BR), various styrene-butadiene copolymer rubbers (SBR), polyisoprene rubber (IR), butyl rubber (IRI), acrylonitrile butadiene rubbers, styrene-isoprene copolymer rubbers, styrene-isoprene-butadiene copolymer rubbers, isoprene-butadiene copolymer rubbers, etc. may be used. These may be used alone or in any blends thereof.
The rubber composition of the present invention contains, as a filler, any carbon black and/or silica normally compounded into rubber compositions. The silica may be a wet type or dry type silica or surface treated silica etc. and is not particularly limited. Even a silica with silanol groups remaining may be used. Further, even carbon black deposited with silica on the surface thereof may be used. The content of the rubber filler is at least 20 parts by weight, preferably 20 to 120 parts by weight, more preferably 40 to 100 parts by weight, based upon 100 parts by weight of the rubber. Silica may also be used as the rubber filler in combination.
The carbon black used in the third aspect of the present invention preferably has a nitrogen specific area (N2SA) of 10 to 200 m2/g and a dibutyl phthalate absorption (DBP) of 50 to 200 cc/100 g, more preferably an N2SA of 130 to 200 m2/g and a DBP of 100 to 150 cc/100 g. The silica preferably has a specific area of 80 to 330 m2/g and a DBP of 110 to 300 cc/100 g, more preferably a specific area of 150 to 250 m2/g and a DBP of 180 to 250 cc/100 g.
The polybutene modified with maleic anhydride used in the third aspect of the present invention is a polybutene containing at least 50 mol % of isobutylene unit and having alkenyl groups and typically is polyisobutylene or a polymer containing isobutylene unit as a main component. The polybutene is a polymer obtained by polymerization of the C4 fraction obtained in the petrochemical field (normally approximately 90% isobutylene and the remainder 1,2-butene, 2,3-butene, etc.) The polybutene obtained from this polymerization may be used in the present invention for the maleic anhydride modification.
In the present invention, the above-mentioned acid anhydride-modified polybutene is compounded in an amount of 3 to 80 parts by weight, preferably 10 to 50 parts by weight, more preferably 15 to 40 parts by weight, based upon 100 parts by weight of the rubber. If the content is too small, the softening effect is not notably manifested, while conversely if too large, time is required for the kneading at the time of processing and the processability tends to be decreased such as a worse roll release.
The rubber composition of the present invention, as explained above, has the polybutene containing the at least 50 mol % of isobutylene unit and having alkenyl groups compound into the composition at the time of compounding the acid anhydride-modified polybutene and the rubber. Typically, an acid anhydride-modified polybutene containing, as a main component, the maleic anhydride-modified polyisobutylene shown by formulae (V) to (VIII), (wherein n is an integer of 1 to 1000 in the formulae (V) to (VIII)) (known polybutene has a number average molecular weight of 200 to 20000) is mixed in.
When mixing the silica into the rubber composition according to the present invention, in the same way as in the prior art, for example, it is possible to use a silane coupling agent in an amount of 5 to 30% by weight of the content of silica. Further, in this case, it is possible to mix a silanol condensation catalyst in an amount of 0.05 to 50% by weight of the content of the silane coupling agent. As the silane coupling agent usable for the silica-containing rubber composition according to the present invention, it is possible to select any silane coupling agent optionally used as a silica filler in the past. As typical examples, vinyl trimethoxysilane, vinyl triethoxysilane, vinyl tris(2-methoxyethoxy)silane, N-(2-aminoethyl)3-aminopropylmethyl dimethoxysilane, N-(2-aminoethyl)3-aminopropyl trimethoxysilane, 3-aminopropyl triethoxysilane, 3-glycidoxypropyl trimethoxysilane, 3-glycidoxypropylmethyl dimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane, 3-methacryloxypropyl trimethoxysilane, 3-mercaptopropyl trimethoxysilane, 3-aminopropyl trimethoxysilane, bis-[3-(triethoxysilyl)-propyl]tetrasulfide, etc. may be mentioned. Among these, bis-[3-(triethoxysilyl)-propyl]tetrasulfide is most preferred from the standpoint of the processability.
The rubber composition according to the third aspect of the present invention may also contain therein various additives generally mixed in for other general rubber use such as vulcanization or cross-linking agents, vulcanization or cross-linking accelerators, various types of oils, antioxidants, fillers, plasticizers, and softening agents. The mixture may be kneaded and vulcanized by a general method to produce the composition which may in turn be used for the vulcanization or cross-linking. The contents of the additives may be made the general contents of the prior art in so far as the objects of the present invention are not impaired.
The rubber composition according to the present invention may be used not only for tires, but also for belts, hoses, rubber shock absorbers, rollers, sheet linings, rubberized cloth, seal materials, gloves, fenders, and the like.
According to the fourth aspect of the present invention, the alkoxysilane is introduced at the end of the polymer chain or in the chain of the polyisobutylene, the reinforcement effect with a filler can be improved and, at the same time, it has been found that the moiety capable of forming a hydrogen bond in the molecule (i.e., xe2x80x9chydrogen bondable moiety) (e.g., carboxylic acid, amide, ester, hydroxy group, amino group) is introduced in the polymer, whereby the reinforcement effect is improved due to the so-called pseudo crosslinking between the rubber molecules and the viscoelastic properties and abrasion resistance are improved.
The preferred embodiments according to the fourth aspect of the present invention are as follows:
(1) A polymer comprising isobutylene, as at least one monomer, and having an alkoxysilane and at least one hydrogen bondable moiety selected from the group consisting of a carboxylic acid, amide, ester, hydroxyl group and amino group in the polymer thereof.
(2) A polymer comprising isobutylene, as at least one monomer, and having an alkoxysilane, carboxylic acid and amide in the molecule thereof.
(3) A polymer comprising isobutylene, as at least one monomer, and having the structure, in, or at the end of, the molecule thereof, of the formula (IX): 
xe2x80x83wherein R7, R8, R9 and R10 may be the same or different, R7 is a C1-C18 hydrocarbon group, R9, R10 and R11 are a C1-C18 hydrocarbon group or a C1-C18 alkoxy group and R11 is a hydrogen atom or a C1-C18 hydrocarbon group.
(4) A rubber composition comprising at least one polymer mentioned above.
As a polymer having isobutylene as at least one monomer usable in the fourth aspect of the present invention, polyisobutylene, polybutene, butyl rubber, brominated butyl rubber, isobutylene-maleic anhydride copolymer, isobutylene-p-methyl styrene-p-bromomethyl styrene copolymer, etc. may be mentioned. These may be used alone or in any mixture thereof.
The modified polybutene(polyisobutylene) according to the present invention are those obtained by introducing a compounds having an alkoxysilane and the hydrogen bondable group such as carboxylic acid, amide, ester, hydroxyl group and amino group to the end or the inside of the polymer containing isobutylene as at least one monomer as mentioned above by a well-known method in this art.
Typical examples of the modified polybutene(polyisbbutylene) are those having the following structures in the main unit thereof. 
In the above formulae, Et is xe2x80x94C2H5 (i.e., ethyl group), Me is xe2x80x94CH3 (i.e., methyl group), Ph is xe2x80x94C6H5 (i.e., phenyl group).
The modified polybutene(polyisobutylene) according to the present invention is compounded into 100 parts by weight of a rubber generally used as a rubber composition in the past, especially, a starting diene rubber, in an amount of 0.1 to 100 parts by weight, preferably 1 to 50 parts by weight. If the content is too small, there is a tendency exhibiting no noticeable intended effect, whereas if too large, the tan xcex4 balance and the abrasion resistance are undesirably decreased.
The rubbers compounded into the rubber composition according to the present invention are diene rubber generally used in rubber compositions in the past. Specifically, for example, natural rubber (NR), various butadiene rubbers (BR), various styrene-butadiene copolymer rubbers (SBR), polyisoprene rubber (IR), butyl rubber (IRI), acrylonitrile butadiene rubbers, styrene-isoprene copolymer rubbers, styrene-isoprene-butadiene copolymer rubbers, isoprene-butadiene copolymer rubbers, etc. may be used. These may be used alone or in any blends thereof.
The rubber composition of the present invention contains, as a filler, any carbon black and/or silica normally compounded into rubber compositions. The content of the rubber filler is at least 10 parts by weight, preferably 15 to 120 parts by weight, based upon 100 parts by weight of the rubber. When the content of the rubber filler is too small, the necessary reinforcement effect for the rubber composition cannot be obtained.
When mixing the silica into the rubber composition according to the present invention, in the same way as in the prior art, for example, it is possible to use a silane coupling agent in an amount of 5 to 30% by weight of the content of silica. Further, in this case, it is possible to mix a silanol condensation catalyst in an amount of 0.05 to 50% by weight of the content of the silane coupling agent. As the silane coupling agent usable for the silica-containing rubber composition according to the present invention, it is possible to select any silane coupling agent optionally used as a silica filler in the past. As typical examples, vinyl trimethoxysilane, vinyl triethoxysilane, vinyl tris(2-methoxyethoxy)silane, N-(2-aminoethyl)3-aminopropylmethyl dimethoxysilane, N-(2-aminoethyl)3-aminopropyl trimethoxysilane, 3-aminopropyl triethoxysilane, 3-glycidoxypropyl trimethoxysilane, 3-glycidoxypropylmethyl dimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane, 3-methacryloxypropyl trimethoxysilane, 3-mercaptopropyl trimethoxysilane, 3-aminopropyl trimethoxysilane, bis-[3-(triethoxysilyl)-propyl]tetrasulfide, etc. may be mentioned. Among these, bis-[3-(triethoxysilyl)-propyl]tetrasulfide is most preferred from the standpoint of the processability.
The rubber composition according to the present invention may also contain therein various additives generally mixed in for other general rubber use such as vulcanization or cross-linking agents, vulcanization or cross-linking accelerators, various types of oils, antioxidants, fillers, plasticizers, and softening agents. The mixture may be kneaded and vulcanized by a general method to produce the composition which may in turn be used for the vulcanization or cross-linking. The contents of the additives may be made the general contents of the prior art in so far as the objects of the present invention are not impaired.
The rubber composition according to the present invention may be used not only for tires, but also for belts, hoses, rubber shock absorbers, rollers, sheet linings, rubberized fabric, seal materials, gloves, fenders, and the like.